HORMONAL ALTERATIONS DURING PROLONGED EXERCISE FOLLOWING ACUTE PLASMA VOLUME EXPANSION 1035

Abstract

To examine whether acute expansion of plasma volume (PV) can modulate the hormonal response to prolonged exercise as observed during a training-induced hypervolemia, 8 untrained males (˙VO2max = 45.4±2.2 ml/kg/min, [horizontal bar over]X±S.E.) cycled for 120 min at 44%˙VO2max following PV expansion (Macrodex) of either 22% (H), 14%(L) or 0% (C). With the exception of Insulin (INS) and α-atrial natriuretic peptide (α-ANP), PV expansion blunted the exercise-induced increase in aldosterone (ALDO), vasopressin (VASO) and the catecholamines, epinephrine (EPI) and norepinephrine (NOREPI). Only in the case of ALDO was the decrease related to the magnitude of the PV expansion, where at 120 min ALDO concentrations (pg/ml) were 660±71, 490±85 and 365±78 (C>L>H p<0.05). Expansion of PV increased (p<0.05) resting blood α-ANP (4.46±0.60, 6.19±0.98, 6.70±0.45 pg/ml for C, L and H, respectively), an effect which persisted throughout exercise. The exercise-induced reduction in INS was not affected by PV expansion. It is concluded that in spite of the dilutional decrease in arterial O2 content, exercise ˙VO2 can be preserved with smaller increases in blood hormonal concentrations.